It is common practice to subtitle motion picture films by etching the emulsion of the developed film by a chemical method. In that case, the film emulsion is etched chemically in zones where symbols, descriptions, or text are to be added leaving the backing medium intact. Various types of chemical method are in existence, however all of them require a large number of manipulations, thereby impeding automation and preventing the total time taken to implement the method from being reduced.
More particularly, in a conventional chemical subtitling method, the surface of the emulsion of a film duplicate is initially coated with a protective layer, then the subtitled text is marked by means of plates in relief. The duplicates of the films are then passed through an appropriate reagent bath which destroys the emulsion at the locations marked by the plates. The protective layer is then removed from the duplicates either by being dissolved or by washing. Various types of washing arrangements are known in the art as represented, for example, by the washing arrangements depicted in FIGS. 1 and 2 herein. As shown in FIG. 1, a film 5 flows from a reel 8 through a washing unit 10 defined by a container 11 and then is wound upon another reel 12. Washing unit 10 can include heating units 15 and/or an ultrasound generating unit 18 in a manner known in the art. In the conventional washing arrangement shown in FIG. 2, a film 25 extends between an unwinding reel 28 and a winding reel 32. Between reels 28 and 32 is positioned a tank 31. Above tank 31 is positioned a spraying unit 35 including a plurality of nozzles 37 for applying jets of washing liquid upon film 25.
After rinsing and drying, the subtitles appear completely transparent and can easily be read when the films are projected.
In spite of the quality of the results obtained, chemical type subtitling methods are penalized by the slowness of the treatment, the need to establish artwork and plates of very high quality, its sensitivity to the accuracy with which various parameters are adjusted such as the relief and the pressure of the plates, the problem of choosing reagents and of irregularities in adhesion and in consistency of the protective layer, the need to take account of the sensitivity and the defects of the emulsions of the prints to be subtitled, and the slowness and the instability of the mechanical engagement between the plate and the film.
The various factors mentioned above thus make implementing a chemical type subtitling method relatively expensive and difficult to automate.
Proposals have also been made to mark motion picture films by means of a high energy laser beam which causes the film emulsion to be ablated locally. The laser beam can be applied through a mask or it may be deflected so as to travel along a determined path corresponding to the inscriptions to be formed on the film. For example, one known motion picture film marking arrangement is shown in FIG. 3 wherein a film 45 is caused to move in the direction of arrow F under a laser beam 48. As is known in the art, laser beam 48 creates subtitles or other markings on film 45 as film 45 passes thereunder. Laser beam 48 is created by a laser unit 50. The output from laser unit 50 is directed to an optical focusing and deflection system 55 which properly positions laser beam 48 in two dimensions, i.e., in both X and Y coordinate planes. Laser unit 50 and optical focusing and deflection system 55 are controlled by means of a control unit 60. More specifically, the output power of laser unit 50 is controlled by control unit 60 by signals outputted through control line 62. In a similar manner, optical focusing and deflection system 55 receives control signals from control unit 60 through control lines 64 and 65 in order to properly position laser beam 48.
In laser subtitling methods, the quality of the result depends on the nature of the emulsion and on the background density of the images on which the subtitles are to be etched. In practice, it has been observed that it is impossible to maintain inscriptions having strokes of constant width under normal working conditions, i.e. with long films having images of varying color and contrast and having emulsions of various characteristics. The working parameters, and in particular the power of the laser beam radiation applied to the film and the displacement speed of the laser beam can be adjusted over ranges of values that are quite large but that depend strongly on the emulsion, thereby making it difficult to obtain subtitles that are sharp and pleasant in appearance using only one pass of the laser beam on the film.
In known laser subtitling methods, the power, the exposure time, and the wavelength are selected so as to destroy the emulsion completely at points where the laser beam strikes the film. The laser etching performed using such a method is nevertheless of non-uniform quality. Thus, there often remain dark zones and spots that are colored to a greater or lesser extent due to gelatinous residues or to damage to the surface of the backing medium which is difficult to control with certain types of media, in particular those made of polyester.
Implementing laser beams of non-negligible power suitable for enabling the emulsion to be etched sufficiently at a working speed that is not too slow gives rise to equipment that is expensive, that consumes a large quantity of electricity and of cooling water, and that requires laser sources to he used that are relatively fragile.
The present invention seeks specifically to remedy the above-mentioned drawbacks and to enable subtitling operations to be performed on motion picture films quickly, cheaply, and automatically while nevertheless obtaining results of good quality with subtitles that are sharp and free from projections, spots, or grayish zones.